Chemical mechanical planarization pad and method of use thereof

ABSTRACT

A web-style polishing pad includes a guide layer through which individual polishing elements protrude on one side and a flexible under-layer attached to the other side. The polishing elements may be affixed at their base to the compressible under-layer and pass through corresponding holes in the guide layer so as to be maintained and translatable in a substantially orthogonal orientation with respect to a plane defined by the guide layer.

RELATED APPLICATIONS

This application is a Continuation-in-Part of and claims priority to:

-   -   (1) U.S. patent application Ser. No. 11/697,622, filed 6 Apr.        2007, which is U.S. National Stage of and claims priority        to: (a) PCT/US05/35979, filed 5 Oct. 2005, which claims the        priority benefit of and incorporates by reference U.S.        Provisional Application 60/616,944, filed 6 Oct. 2004, and U.S.        Provisional Application 60/639,257, filed 27 Dec. 2004; and (b)        PCT/US05/35732, filed 5 Oct. 2005, which claims the priority        benefit of and incorporates by reference U.S. Provisional        Application No. 60/631,188, filed 29 Nov. 2004, and U.S.        Provisional Application No. 60/639,257, filed 27 Dec. 2004;    -   (2) U.S. patent application Ser. No. 11/576,942, filed 9 Apr.        2007, which is a U.S. National Stage of and claims priority to        PCT/US05/35660, filed 5 Oct. 2005, which claims the priority        benefit of and incorporates by reference U.S. Provisional Patent        Application No. 60/631,189, filed 29 Nov. 2004 and U.S.        Provisional Patent Application No. 60/639,257, filed 27 Dec.        2004;    -   (3) U.S. patent application Ser. No. 11/576,944, filed 9 Apr.        2007, which is a U.S. National Stage of and claims priority to        PCT/US05/35978, filed 5 Oct. 2005, which claims the priority        benefit of and incorporates by reference U.S. Provisional Patent        Application No. 60/631,187, filed 29 Nov. 2004 and U.S.        Provisional Patent Application No. 60/636,055, filed 14 Dec.        2004;    -   (4) U.S. patent application Ser. No. 11/562,310, filed 21 Nov.        2006, which is a non-provisional of, claims priority to and        incorporates by reference U.S. Provisional Patent Application        No. 60/739,252, filed 23 Nov. 2005; and U.S. Provisional Patent        Application No. 60/758,006, filed 10 Jan. 2006;    -   (5) U.S. patent application Ser. No. 11/562,346, filed 21 Nov.        2006, which is a non-provisional of, claims priority to and        incorporates by reference U.S. Provisional Patent Application        No. 60/784,263, filed 21 Mar. 2006; and    -   (6) U.S. patent application Ser. No. 11/846,304, filed 28 Aug.        2007, and is also a non-provisional of and claims priority to        U.S. Provisional Patent Application 60/969,684, filed 3 Sep.        2007, all of the above of which are incorporated herein by        reference.

FIELD OF THE INVENTION

The present invention relates to the field of chemical mechanicalplanarization (CMP) and to a CMP polishing pad utilized in CMPprocessing on web platform, in one instance a pad having uniform or nearuniform polishing performance across its surface.

BACKGROUND

In modem integrated circuit (IC) fabrication, layers of material areapplied to embedded structures previously formed on semiconductorwafers. Chemical mechanical planarization (CMP) is an abrasive processused to remove or flatten these layers and polish the surface of a waferto achieve the desired structure. CMP may be performed on both oxidesand metals and generally involves the use of chemical slurries appliedvia a polishing pad that is moved relative to the wafer (e.g., the padmay rotate circularly relative to the wafer). The resulting smooth, flatsurface is necessary to maintain the photolithographic depth of fieldfor subsequent processing steps and to ensure that metal interconnectsare not deformed over contour steps Damascene processing requires CMP toremove metals, such as tungsten or copper, from the top surface of adielectric to define interconnect structures.

The planarization/polishing performance of a polishing pad and slurrycombination is impacted by, among other things, the mechanicalproperties and slurry distribution ability of the polishing pad and thechemical properties and distribution of the slurry. Often a polishingpad may be porous and/or include grooves to distribute the slurry acrossits surface. However, this reduces the overall strength of the polishingpad, making it more flexible and thus reducing its planarizationcharacteristic. Typically, hard (i.e., stiff) pads provide goodplanarization, but are associated with poor with-in wafer non-uniformity(WIWNU) film removal. Soft (i.e., flexible) pads, on the other hand,provide polishing with good WIWNU film removal characteristics, but poorplanarization characteristics. In conventional CMP systems, therefore,harder pads are often placed on top of softer pads to improve WIWNU.Nevertheless, this approach tends to degrade planarization performancewhen compared to use of a hard pad alone.

FIG. 1A illustrates “dishing” as a result of applying a flexiblepolishing pad to wafer 100. The flexible polishing pad provides for asmooth surface but creates dishing 106 by over-polishing softerelements, such as copper layer 104, on the surface of substrate 102. Theconsequence of dishing is an undesirable loss of metal thickness,leading to poor device performance.

Dishing can be reduced or eliminated through the use of a stifferpolishing pad, which can provide greater planarization. Pads may be madestiffer by reducing the number of pores and/or grooves in the pad,however, this can lead to different consequences, for example poorslurry distribution. The net effect may be to increase the number ofsurface defects 108 on the substrate 102 and/or copper layer 104 (e.g.,by scratching and/or pitting the surface/layer), as shown for example inFIG. 1B which illustrates surface defects 108 that may result fromapplication of a relatively stiff polishing pad to wafer 100.

Variations in the above-described effects may also be present atdifferent points across a wafer. FIG. 1C shows a cross-section of awafer 100′ having multiple dies thereon. Assume that a copper layer ispresent on the top surface of wafer 100′ and that FIG. 1C illustratesthe wafer after CMP polishing with a hard pad has occurred. As can beseen, for those dies closer to the center of wafer, the effects ofdishing 110, 114 and erosion 112, 116 are less severe than for dies nearthe edge of the wafer. This is due to the fact that the hard pad mustcompensate for WIWNU by over-polishing the dies that clear first (i.e.,those near the edge of the wafer 100).

FIG. 1D illustrates the surface of a post-CMP wafer 100″ after polishingwith a stacked pad (i.e., one in which a hard pad is placed over asofter pad). In this instance the dishing and erosion of the features atcenter and edge of the wafer (110″, 112″ and 114″, 116″, respectively)is more severe than occurs near the center of the wafer 100′ illustratedin FIG. 1C, but less so than occurs near the edge thereof. This is dueto the fact that while the softer under-pad degrades planarization,polishing is more uniform, leading to more consistent overallperformance across the entire surface of the wafer.

It is therefore the case that designing CMP polishing pads requires atrade-off between WIWNU and planarization characteristics of the pads.This trade-off has led to the development of polishing pads acceptablefor processing dielectric layers (such as silicon dioxide) and metalssuch as tungsten (which is used for via interconnects in subtractiveprocessing schemes). In copper processing, however, WIWNU directlyimpacts over-polishing (i.e., the time between complete removal ofcopper on any one area versus complete removal from across an entirewafer surface) and, hence, metal loss and, similarly, planarization asexpressed by metal loss. This leads to variability in the metalremaining in the interconnect structures and impacts performance of theintegrated circuit. It is therefore necessary that both planarity andWIWNU characteristics of a pad be optimized for best copper processperformance.

Conventional polishing pads are typically made of urethanes, either incast form and filled with micro-porous elements or from non-woven feltcoated with polyurethanes. During polishing, the pad surface undergoesdeformation due to polishing forces. The pad surface therefore has to be“regenerated” through a conditioning process. The conditioning processinvolves pressing a fine, diamond covered disc against the pad surfacewhile the pad is rotated much like during the polishing processes. Thediamonds of the conditioning disc cut through and remove the top layerof the polishing pad, thereby exposing a fresh polishing pad surfaceunderneath.

These concepts are illustrated graphically in FIGS. 2A-2C. Inparticular, FIG. 2A illustrates a side cutaway view of a new polishingpad 200. Polishing pad 200 contains microelements 204 and grooves 206,much like those found in commercially available polishing pads such asthe IC1000 of Rhom & Haas, Inc. FIG. 2B shows the surface 202 ofpolishing pad 200 after polishing. The top surface of the pad showsdegradation 208, especially around the microelements 204 where the edgesare degraded due to plastic or viscous flow of the bulk urethanematerial. FIG. 2C shows the surface 202 of the polishing pad after aconditioning process has been completed. Note the depth of grooves 206is lower than was the case for the new pad illustrated in FIG. 2A due tomaterial removal during conditioning.

Over multiple cycles of polishing and conditioning, it is usually thecase that the overall thickness of a pad wears up to a point such thatthe pad needs to be replaced. It is evident to those practicing in theart that pad wear rates differ from pad to pad and may also differ fromone batch of pads to another batch. This often leads to variation in CMPperformance over the life time of the pad and variation is also observedpad to pad. Frequent changes in pads also lead to reduced productivityof the overall process

One method to achieve stable polish performance and increaseproductivity is known as web processing. In web processing, a roll ofpad is supplied to the polish table through a series of rollers, notablya feed roller and an uptake roller. CMP machines which use web pads anddetails of processing wafers with this process are discussed in U.S.Pat. Nos. 5,335,453, 6,244,935, 6,379,231, and 6,398,630.

U.S. Pat. No. 5,335,453 describes a machine which uses a feed rollercontaining new pad material and a uptake roller containing used padmaterial. A polish table is positioned between the two rollers. Theportion of pad material currently in use is situated over the polishtable for polishing wafer substrates and to effect material removaltherefrom.

U.S. Pat. No. 6,244,935 describes a rotary polish table which alsocontains a feed roller and an uptake roller to enable polishing in muchthe same fashion as a conventional rotary polish system while allowing aweb pad to be installed on the rollers for longer use. A new pad roll ismounted onto the feed roller, applied across the polish table, whichcontains multiple vacuum channels, and fed onto the uptake roller. Aswafers are processed, the pad is advanced by a predetermined amount suchthat a segment of fresh pad (i.e., a fraction of the total pad) is fedover the polish table and a corresponding segment of used pad is removedby uptake onto the uptake roller.

Not all polishing pads can be formed into rolls for use with webprocessing CMP equipment. For example, stiff pads (such as IC padssupplied by Rohm & Haas) cannot be easily formed into a roll, yet, asdiscussed above, the inherent stiffness of such pads is required if goodplanarization characteristics are desired. CMP pads for planarizationoffered by other manufacturers, such as the D100 pads offered by CabotCorp. and the FAST™ polishing pads produced by PPG Industries, havesimilar limitations. There are, therefore, significant constraints withrespect to implementing web-style CMP equipment architectures.

SUMMARY OF THE INVENTION

Disclosed herein is a polishing pad, which, while being capable ofpolishing like a hard pad, can be formed into a roll that can beinstalled onto conventional web-style CMP polishing equipment.

A polishing pad configured in accordance with an embodiment of thepresent invention includes a sheet of guide layer having optionallyaffixed thereto a porous slurry distribution layer on one side and aflexible under-layer on the other side. A plurality of polishingelements inter-digitated with one another through the slurrydistribution layer and the guide layer, so as to be maintained in planarorientation with respect to one other and the guide layer, are affixedto the flexible under-layer with each polishing element protruding abovethe surface of the guide layer to which the optional slurry distributionlayer is adjacent. The collective materials can be rolled onto acylindrical support

The guide layer of the polishing pad may be made of a Mylar™ orpolycarbonate or other suitable polymer material and includes holes inwhich individual polishing elements are accommodated. The polishingelements may have any shape such as circular, triangular, square,polygon or any other shape. A combination of shapes and sizes maybe usedon the same pad roll. The polishing elements may be made from solid ormicro-porous polymer and may also include a metal oxide material. Thepolishing elements may be made from a polymer, such as polyurethane,ABS, SAN, or poly acrylonitrile, and may include micro-pores or a metaloxide, such as aluminum oxide, silicon dioxide, and/or titanium dioxide.

One or more of the polishing elements may be fashioned so as to have acylindrical body, with or without a circular base having a diameterlarger than that of the cylindrical body. The top surface of thepolishing elements may be flat or have a predetermined patternincorporating micro-features. The under-layer may be made frompolyurethane or other flexible materials such as PVA, Teflon™,polyethylene, PVDF, neoprene, styrene butadiene rubber, or EPDM. Thecomposite pad is preferably used in conjunction with a compressible foamto enable full movement of the polishing elements in a directionorthogonal to a plane defined by the guide layer.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention is illustrated by way of example, and notlimitation, in the figures of the accompanying drawings, in which:

FIGS. 1A-1D illustrate the effects of dishing and erosion due toinconsistent planarization across a wafer during CMP operations.

FIGS. 2A-2C illustrate examples of pad wear experienced by conventionalpolishing pads.

FIG. 3A is a cut-away side view of a polishing pad configured inaccordance with one embodiment of the present invention for use in CMPoperations.

FIG. 3B illustrates a polishing pad similar to that shown in FIG. 3A,but which includes a compressible under layer in accordance with afurther embodiment of the present invention.

FIG. 3C is a side view of a polishing pad configured in accordance withan embodiments of the present invention and employed in a web-stylepolishing apparatus.

FIG. 3D is a side view of a polishing pad configured in accordance withan embodiment of the present invention with a wafer in proximitythereto.

FIG. 4 is a top view of a polishing pad having inter-digitated polishingelements between which slurry may flow in accordance with still anotherembodiment of the present invention.

FIG. 5 is a diagram showing a sequence for manufacturing a polishing padsuited for use with web-style polishing apparatus in accordance with anembodiment of the present invention.

DETAILED DESCRIPTION

Described herein are improved CMP polishing pads formed in sheetssuitable for web-style CMP processing equipment, methods ofmanufacturing same, and processes for polishing semiconductor wafers andstructures layered thereon, including metal damascene structures, usingsuch polishing pads. As indicated above, it is known that a moreflexible polishing pad produces dishing while a harder pad (with reducedslurry distribution ability) produces more surface defects. At the sametime, it has been demonstrated that pads applied in web-form providemore uniform processing performance and higher productivity in CMPprocesses. Conventional hard pads cannot be provided in roll form forsuch web-style applications, as the hardness of polishing layer limitsthe ability to physically roll the pad without damaging it. The paddesign disclosed herein overcomes this limitation and enables higherproductivity.

Although various polishing pad configurations (e.g., with specificexamples of geometric ranges, ratios, and materials) and polishingprocesses are described herein, it should be appreciated that thepresent invention can be equally applied to encompass other types ofpolishing pad fabrication materials and deposition removal techniques.Stated differently, the use of such other materials and techniques aredeemed to be within the scope of the present invention as reflected inthe claims following this description.

The above-referenced related patent applications, which are assigned tothe assignee of the present invention, discuss polishing pad designswhich use independent polishing elements to effect uniform polishing ofwafers and the like. Like the polishing pads discussed in thoseapplications, a polishing pad configured in accordance with the presentinvention and suitable for use with web-style processing apparatus has aguide plate which is affixed to a porous slurry distribution layer onone side and a compressible under-layer on the other side. A pluralityof polishing elements interdigitated with one another are affixed to thecompressible under-layer and protrude through the guide plate and theslurry distribution layer, so as to be maintained in planar orientationwith respect to one other and the guide plate. Optionally, a membranemay be positioned between the guide plate and the slurry distributionlayer. Such a membrane may be conductive or non-conductive and may befastened to the guide plate by an adhesive. In some cases, the membranemay be an ion exchange membrane.

The guide plate of the present polishing pad may be made of anon-conducting material and may include holes in which individualpolishing elements are accommodated. Some of the polishing elements mayhave circular cross sections, while others may have triangular crosssections, square cross-sections, hexagonal cross-sections, or any othershape. In any event, the polishing elements may be made from any one orcombination of: a thermally conducting material, an electricallyconducting material, or a non-conducting material. For example, thepolishing elements may be made of a conductive polymer polyaniline,carbon, graphite, or metal-filled polymer. One or more of the polishingelements may be fashioned so as to make sliding contact with a wafersurface during polishing operations, while others may be fashioned so asto make rolling contact with a wafer surface (e.g., with a rolling tipmade of a polymeric, metal oxide, or electrically conducting material)during such operations.

The slurry distribution material may include a number of slurry flowresistant elements (e.g., pores) and be between 10 and 90 percentporosity. Preferably, though not necessarily, the slurry distributionmaterial is fastened to the guide plate by an adhesive (e.g., inaccordance with the manufacturing process discussed below). In somecases the slurry distribution material may include multiple layers ofdifferent materials. For example, the slurry distribution material mayinclude a surface layer having relatively large pores and a lower layerhaving relatively small pores. It is conceivable that the slurrydistribution element and guide plate functions can be performed by asingle material. Such a material may be a guide plate having a open porefoam surface or grooves or baffles to modulate the slurry flow acrossthe surface.

The polishing pad may also include wear sensors configured to provideindications of pad wear and/or end-of-life. For example, the polishingpad may include one or more pad wear sensors embedded at a depth from atop surface of the pad as measured from a working end of one or more ofthe polishing elements. The pad wear sensor(s) may be an opticallytransparent plug having a top surface covered with reflective coating; anumber of optically transparent plugs embedded to different depthswithin the pad; an optically transparent conical plug mounted flush withthe top surface of the pad surface; an optically transparent plug havinga multi-step surface configured to be exposed to varying degrees as thepad wears; or an optically transparent plug containing screens withvarying degrees of transmission arranged in order of reflectivity. Instill further embodiments, the pad wear sensor(s) may be anelectrochemical sensor containing two or more probes embedded in thepad, or a conductive plate embedded at a depth below the surface of thepad.

In order to provide for the web-style environment in which the presentpad is intended for use, some flexibility must be maintained. The use ofdiscreet, hard polishing elements distributed over a flexible layer notonly enables uniform polishing of wafer surfaces but also permits thepad to be rolled into a form suitable for use with web-style apparatus.Preferably, the overall thickness of the web-style pad is less than 50mils and, in some cases, less than 25 mils. Total pad thickness isdetermined by adding the thickness of the flexible under-layer andpolishing elements together, while the pad life is determined by thethicknesses of the polishing elements and guide layer. In someembodiments, the present web pad uses polishing elements having a heightof less than 40 mils and flexible under-layer having a thickness of lessthan 10 mils to achieve total thickness of less than 50 mils. The guidelayer may be on the order of 5-10 mils thick.

The pad stack may be combined with an external compressible foam layerto help ensure uniform polishing. One suitable compressible under-layeris polyurethane foam, marked under the brand name PORON™ and availablefrom Rogers Corporation. Conventional polishing pads use thicknesses ofabout 62 mils for such compressible foam layers.

The material which makes up the flexible under-layer of the presentpolishing pad is selected to provide compliance and to contain thepolishing elements. The under-layer material is selected such that itdoes not interfere with independent operation of the polishing elements.As such its mechanical properties, such as stiffness or hardness andresiliency, are chosen such that when used in conjunction with anexternal compressible foam layer, the properties of under-layer do notalter the overall compressibility and resilience of the compressiblefoam by more than 5-10%. A suitable under-layer material may be lowdensity, low rebound foams 0392 from Rogers Corp. A thin, solid,flexible sheet made from rubber, latex or polyurethane may also be used.

As discussed further below, the guide layer of the present pad limitsmovement of the polishing elements to a plane orthogonal to that of theguide layer itself (i.e., towards or away from the wafer beingpolished), and may be made of suitably flexible material, such as a thinlayer of Mylar™ or polycarbonate. The guide layer also functions as acarrier layer for the pad structure across rollers of the web-stylepolishing apparatus.

The polishing pads described herein may be used in a variety of stepsassociated with CMP processing. This includes utilization in amulti-step process, wherein multiple polishing pads and slurries ofvarying characteristics are used in succession, to one step processes,where one polishing pad and one or more slurries are used throughout theentire polishing phase. Alternatively, or in addition, a pad configuredwith hard (>Shore D 45) polyurethane polishing elements may be suitablefor planarizing steps while a pad with polishing elements made fromsofter polymer (<shore D 45) such as polyurethane, PVA etc. may besuitable for buffing and cleaning steps.

Referring now to FIG. 3A, a cut-away side profile view of a circularpolishing pad 300 used in CMP processing and configured according toembodiments described in the above-cited related patent applications. Asshown, polishing elements 302 protrude through holes in a guide plate304 and are supported by (e.g., affixed to) a base, such as acompressible under-layer 306. In use, the polishing pad 300 rotatesrelative to a wafer surface being polished, and polishing elements 302make contact with that surface. A optional slurry distribution material(not shown) above the guide-layer 304 provides flow control in slurrypathways between the polishing elements 302.

The foundation of polishing pad 300 is the guide plate 304, whichprovides lateral support for the polishing elements 302. The guide platemay be made of a non-conducting material, such as a Mylar™ orpolycarbonate material. In one embodiment of the present invention, theguide plate 304 includes holes fabricated into or drilled out of theguide layer to accommodate each of the polishing elements 302. Thepolishing elements 302 may be fixed to the top of compressibleunder-layer 306 and held in place by an adhesive, such as double sidedtape or epoxy. This leaves the polishing elements 302 free to move in adirection parallel to their long axis (orthogonal to a plane defined bythe guide plate), through the holes in guide plate 304.

As indicated above, the volume between the interdigitated polishingelements 302 may be at least partially filled with a slurry distributionmaterial. The slurry distribution material may include flow resistantelements such as baffles or grooves (not shown), or pores, to regulateslurry flow rate during CMP processing. In varying embodiments, theporous slurry distribution material may have between 10 and 90 percentporosity and may be overlaid on guide layer 304. The slurry distributionmaterial may be fastened to the guide plate by an adhesive, such asdouble sided tape. Additionally, the slurry distribution material mayinclude various layers of differing materials to achieve desired slurryflow rates at varying depths (from the polishing surface) of the slurrydistribution material. For example, a surface layer at the polishingsurface may have larger pores to increase the amount and rate of slurryflow on the surface while a lower layer has smaller pores to keep moreslurry near the surface layer to help regulate slurry flow.

FIG. 3B shows one embodiment of a web pad 300′ configured in accordancewith the present invention. Web pad 300′ is similar in construction topad 300 described with reference to FIG. 3A, but includes a thinflexible under-layer 308 to contain the polishing elements 302. Thecompressible under-layer 306 is external to the pad stack (whichincludes the polishing elements, the flexible under-layer and the guidelayer 304). The compressible under-layer 306 serves the same function asthat in pad 300 and provides, among others features, a positive pressuredirected toward the polishing surface of the pad when compressed.Typically, the compression may vary around 10% at 5 psi (pounds persquare inch), however, it will be appreciated that the compression maybe varied dependent upon the materials used in constructing polishingpad 300′ and the type of CMP process. For example, the compressibleunder-layer 306 may be formed of BONDTEX™ foam made by RBX Industries,Inc. or Poron™ Performance Urethane made by Rogers Corp. In varyingembodiments, the compressible under layer 306 is provided externally andis not part of the web pad roll.

FIG. 3C illustrates a cut-away side profile view of polishing pad 300′as used in CMP processing, according to one embodiment of the presentinvention. In use, the polishing pad 300′ is fed from a roll on a feedroller 312 over the top of a polishing table 310 and onto an uptakeroller 314. The relative motion between wafer and polishing table isprovided by motion of either one or both the polishing table and/orwafer. Notice that compressible under-layer 306 is not part of the webpad roll and, instead, is applied over the surface of the polishingtable 310. In other cases, the flexible under-layer 306 may be part ofthe web pad stack.

FIG. 3D illustrates a further embodiment of the present web pad 300′ andshows a wafer 320 being polished. Wafer 320 contacts the polishingelements 302 and is moved relative to the pad by rotating either or bothpad 300′ and/or wafer 320. For example, the feed roller 312 and theuptake roller 314 may be affixed to sides of the polishing table 310,and the entire polishing table rotated relative to wafer 320.alternatively, or in addition, wafer 320 may be supported by a waferstage that is rotated relative to polishing table 310.

FIG. 4 illustrates a top down view of a portion of a polishing pad 400configured according to one embodiment of the present invention.Polishing elements 406 are interdigitated throughout polishing pad 400.A slurry distribution material 404 is permeated throughout the volumecreated by polishing elements 406 protruding from the guide layer (notshown). While the volume provides a slurry path, the slurry distributionmaterial provides a mechanism to control slurry flow throughout thevolume as discussed above.

The distribution of the polishing elements 406 may vary according tospecific polishing/process requirements or characteristics. In varyingembodiments, the polishing elements 406 may have a density of between 30and 80 percent of the total polishing pad surface area, as determined bythe diameter (D) of each polishing elements 406 and the area of thepolishing pad 400. In one embodiment, the diameter D is at least 50micrometers. In other embodiments, the diameter D may vary between 50micrometers and 12 millimeters. Typical diameters of the polishingelements are 3-25 mm.

Various embodiments of the present polishing pad may have polishingelements of at least two different types of materials, each having adifferent coefficient of friction, and arranged over the pad so as toprovide a non-planar material removal profile for the pad. The polishingelements may be arranged to provide an edge-fast, edge-slow, center-fastor center-slow material removal profile. For example, the differentpolishing elements may be arranged in different densities across thepad.

Still another embodiment of the present polishing pad has a plurality ofpolishing elements, some of which are polyurethane and others of whichare Delrin. The polishing elements may be various manners across the padsuch that those of the polishing elements which are Delrin make upapproximately 5-50% of the total number of polishing elements inlocations corresponding to areas of the pad configured to providerelatively lower material removal rates than other areas of the pad. Theoverall density of polishing elements may be uniform per unit area ofthe pad and/or the polishing elements may be laid out in a uniformradial arrangement. In some cases, both the Delrin and polyurethanepolishing elements may have a common shape and size or may havedifferent shapes/sizes.

In still other embodiments, the present polishing pad may include acombination of electrically conductive and electrically non-conductivepolishing elements. The conductive polishing elements may be made of oneor more of a conductive polymer, graphite or combination thereof, whilethe non-conductive polishing elements may be made of a thermoplasticpolymer such as polyurethane, Delrin, nylon, etc. These differentpolishing elements may have the same shape/size or differentshapes/sizes.

Optionally, a membrane may be positioned between the guide layer and theslurry distribution layer. Such a membrane may be conductive ornon-conductive membrane and may be fastened to the guide layer by anadhesive. In some cases, the membrane may be an ion exchange membrane.

Other embodiments of the present polishing pad may have one or morepolishing elements made from a hydrogel material having an intrinsicability to absorb water. The hydrogel material may have nomicro-porosity, a water absorption capability of 4%-60% by weight, a wettensile strength greater than 1000 psi, a flexural modulus greater than2000 psi, and a wet Shore D hardness between 25-80, inclusive. In otherembodiments, the hydrogel material may have a water absorptioncapability of 4%-60% by weight, a microporosity of 1% to 20% by volume,micropores of 20-100 microns, a wet tensile strength greater than 1000psi, a flexural modulus greater than 2000 psi, and a wet Shore Dhardness between 25-80, inclusive. In either instance, the hydrogelmaterial may be made from one or a combination of the following moeties:urethane, alkylene oxides, esters, ethers, acrylic acids, acrylamides,amides, imides, vinylalcohols, vinylacetates, acrylates, methacrylates,sulfones, urethanes, vinylchlorides, etheretherketones, and/orcarbonates.

FIG. 5 shows a web pad manufacturing machine 500 configured inaccordance with an embodiment of the present invention. The machine 500consists of three primary rollers 501, 502 and 503. Roller 501 is usedto provide guide layer 514, roller 502 is used to provide flexibleunder-layer 515, and roller 503 is an uptake roller on which thecompleted pad is collected after being assembled.

In operation, a sheet of guide layer material is mounted on roller 501and passed through an assembly path defined by guide rollers 504, 507and 510. As the guide layer material passes under polishing elementdispensing station 512, polishing elements 513 are placed through holesin the guide layer material. This may be accomplished, for example,while mechanical vibration energy is applied so as to ensure that thepolishing elements 513 extend fully into the holes in the guide layermaterial. Alternately a pick-and-place tool may be used to dispensepolishing elements at predetermined locations in the guide layermaterial. An optional laser or machining system (not shown) may be addedproximate to the guide rollers 507 and 510 to make holes in guide layermaterial 514 for the polishing elements.

As holes in the guide layer material 514 are occupied with polishingelements 513, a first stack 516 is formed. Flexible under-layer 515 isthen attached to this guide layer—polishing element composite. Roller502 supports a sheet of flexible under-layer material 515. That materialis dispensed such that it passes through a path defined by guide rollers505, 508 and 511, which brings the material into contact with theflexible under-layer-polishing element stack 516 to form composite stack517. The flexible under-layer material 515 may be secured to the guidelayer material 514 with an adhesive, which may be applied prior to theunder-layer material 515 coming into contact with the guide layermaterial 514 (not shown in detail).

Not shown in this drawing is the addition of a slurry distributionmaterial or a further compressible foam layer, but these optional layersmay be added in a fashion similar to that discussed above. That is, thematerials may be rolled off of support rollers, through assembly pathsdefined by a series of guide rollers and brought into contact with theguide layer/compressible under layer, as appropriate, and affixedthereto, e.g., by adhesive. The final stack of materials 517 defines thepolishing pad, which may be taken up onto roller 503 through a pathdefined by guide rollers 509 and 506, for example.

Thus, an improved CMP polishing pad, method of manufacturing same andprocess for polishing semiconductor wafers and structures layeredthereon, including metal damascene structures on such wafers, using sucha pad has been described. Although the present polishing pad, processesfor using it and methods for manufacturing same have been discussed withreference to certain illustrated examples, it should be remembered thatthe scope of the present invention should not be limited by suchexamples. Instead, the true scope of the invention should be measured onin terms of the claims, which follow.

1. A polishing pad, comprising a sheet-like guide layer having holestherein, a plurality of individual polishing elements protruding throughsaid holes, and a sheet-like flexible under-layer affixed to the guidelayer so as to maintain the polishing elements in a substantiallyorthogonal orientation with respect to a plane defined by the guidelayer, the polishing elements further being translatable along an axisorthogonal to said plane.
 2. The polishing pad of claim 1, wherein atleast some of the polishing elements are made of one of: solidpolyurethane, micro-porous polyurethane, polyacrylic, or PVA.
 3. Thepolishing pad of claim 1, wherein the guide layer is made of one of:polyester or polycarbonate.
 4. The polishing pad of claim 1, wherein theflexible under-layer is made of one of: silicone, natural rubber,styrene butadiene rubber, neoprene, or polyurethane.
 5. A method ofmaking a polishing pad, comprising depositing a plurality of individualpolishing elements into holes present in a sheet of a guide layermaterial and affixing to the guide layer a backing layer so as tomaintain the polishing elements in a substantially orthogonalorientation with respect to a plane defined by the guide layer.
 6. Themethod of claim 5, further comprising taking up a composite formed bythe guide layer, the backing layer and the polishing elements onto anuptake roller.
 7. The method of claim 5, wherein the backing layer isaffixed to the guide layer by an adhesive.
 8. The method of claim 5,wherein the guide layer material is directed to a position at which thepolishing elements are deposited into the holes by external means. 9.The method of claim 8, wherein the holes are formed after the guidelayer material is spooled off a feed roller.
 10. The method of claim 8,wherein the backing layer is directed to a second position at which itis affixed to the guide layer material by one or more guide rollersdifferent than the guide rollers used to direct the guide layer materialto the position at which the polishing elements are deposited into theholes.